PARTHENIUM HYSTEROPHORUS L., AN ALIEN INVASIVE WEED THREATENING NATURAL VEGETATIONS IN PUNJAB, PAKISTAN

Parthenium (Parthenium hysterophorus L.) is an invasive weed of family Asteracaea, native to Tropical America. This weed has been rapidly spreading in different parts of Pakistan for the last 20 years. Surveys of different areas of the province Punjab viz. Lahore, Sialkot, Nankana Sahib, Hafiz Abad, Okara, Shekhupura, Wah Cantt, and Attock, were carried out during 2006–2010 to evaluate the invasion of parthenium weed in these areas. Generally, ten localities in each area were surveyed. Different parameters of weed distribution viz. prevalence (presence or absence at different localities in an area), frequency (presence or absence at different sites at a locality) and density (number of plants per meter square) were recorded. Parthenium showed 90–100% prevalence in different surveyed areas. The frequency and density of this weed ranged from 36–90% and 1–20 m -2 , respectively in the various studied areas. Present study concludes that parthenium has become a problematic weed in various regions of the Punjab and is rapidly replacing the local flora. High reproductive potential, allelopathic nature, fast growth rate and lack of natural enemies coupled with conducive environmental factors are the major factors responsible for rapid invasion of parthenium in the region. It is the need of the hour to take appropriate measures to contain the further spread of this aggressive weed in the country.